This invention relates to a fuel injection control system for an internal combustion engine and more particularly to an improved control system for coping with transient conditions.
The use of fuel injection and particularly direct cylinder fuel injection seems to be a viable way of coping with the control of exhaust gas emissions and the achievement of high fuel efficiency with internal combustion engines. This is particularly true in conjunction with two cycle, crankcase compression internal combustion engine. However, it is essential to provide an adequate and yet relatively simple control for the amount of fuel and timing of the fuel injected by the fuel injector to achieve the desired results.
The amount of fuel injected by the fuel injector and the timing of the injection is controlled in many injection systems in response to two sensed engine parameters, intake air amount and engine speed. Where these two control parameters are employed there are certain difficulties, however, particularly in conjunction with two cycle engines. In the low load low speed range, such as at idling or when trolling with an outboard motor, it is difficult to stabilize the engine speed because the intake air amount fluctuates. Also, if the fuel control is varied in response to sensed engine speed and intake air amount, there is a time delay between the measuring of these parameters and the calculating of the engine fuel control parameters which can cause a delay in speed change response. This is particularly likely to cause a delay in speed increase when the engine is abruptly accelerated.
In order to eliminate some of the difficulties noted, it has been proposed to provide a fuel injection control system that has control phases relating to the load on the engine. For example, the engine can have control phases which differ depending upon whether the engine is operating in a low, medium or high load ranges. With such systems, when the throttle opening is set to a relatively small value, the engine is determined to be in the low load mode and the fuel control is only determined on the basis of engine speed without relation to intake air amount. As a result, the fluctuations resulting from the changes in intake air amount are eliminated. However, when the engine throttle is opened to a larger extent such as to indicate high load, then the fuel control is determined only on the basis of intake air amount regardless of actual engine speed. When the engine is operating in the mid range, the fuel control is determined by a mixture of the engine speed and intake air amount.
It should be understood that it would be possible, to provide a system that measures all parameters of the engine and contains a plurality of maps so as to provide the ideal fuel control under all conditions. However, such an arrangement would employ an extremely expensive and complicated computer and hence is not practical for large volume usage.
A system of control where the engine is operated by a control strategy as aforedescribed depending upon the load range, there are still some problems. These problems occur during transient conditions when the engine is being abruptly accelerated or decelerated. For example, when the engine is operating at a high speed and is abruptly decelerated, if the deceleration brings the speed of the engine into the low load range, then the control parameters are changed at once to values for lowering the engine speed and may cause the engine to be stalled. If the deceleration is into the medium load range and the fuel control parameters are varied relating to intake air amount and engine speed, the reaction time is slow due to the delay of measuring of the intake air amount and the engine speed will not be reduced smoothly from high speed to a lower speed.
Problems also can occur when the engine is operating at low speeds and is abruptly accelerated. If the acceleration is into the medium load range and the engine fuel control is then varied relative to intake air amount and engine speed, the reaction time again is slow due to the delay in the amount of intake air detection and the speed is not raised in a smooth manner.
There are also systems which do not divide the load conditions into three loads, as aforenoted, but only two loads, high load and low load. These systems also have the disadvantages already noted.
It is, therefore, a principal object to this invention to provide an improved fuel control system for a fuel injected internal combustion engine.
It is another object to this invention to provide a fuel control system for a fuel injected internal combustion engine that is relatively simple in operation and requires a minimum number of sensed conditions for the fuel control.
It is a yet further object to this invention to provide a fuel control system for a fuel injection unit of an internal combustion engine that improves the performance under transient conditions and still is able to be relatively simple and uncomplicated.